1. Field of the Invention
The present invention relates to a wafer grinding apparatus, and more specifically, to a wafer backside grinding apparatus capable of preventing cross-shaped flaws from forming in the wafer.
2. Description of the Prior Art
A wafer grinding apparatus is used for grinding a back-side of a semiconductor wafer, so that a thickness of the wafer can be well controlled for facilitating the following packaging processes. Generally, the wafer grinding apparatus includes a positioning table for adjusting an orientation of the wafer, grinding tables where a wafer grinding process is performed, and a spinner table where a cleaning process is performed. Additionally, the wafer grinding apparatus further includes a wafer-transporting device for transferring the wafer from one table to another table. Since the wafer-transporting device contacts the semiconductor wafer frequently, the wafer-transporting device should be well designed for preventing the semiconductor wafer from being damaged.
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a schematic diagram of a wafer-transporting device of a wafer grinding apparatus according to the prior art. FIG. 2 is a schematic diagram illustrating a wafer having a cross-shaped flaw thereon. As shown in FIG. 1, a prior art wafer-transporting device 10 includes a suction pad 12 for sucking a wafer 16 through vacuum suction, and a transporting arm 14 connected to the suction pad 12 for transferring the wafer 16 sucked by the suction pad 12. Additionally, the suction pad 12 comprises a ceramic material so that an upper surface 12a and a lower surface 12b of the suction pad 12 are both quite hard.
Generally, a wafer backside grinding process is performed in the wafer grinding apparatus for grinding a backside of the wafer 16. As a result of the wafer backside grinding process, a thickness of the wafer 16 can be reduced to 30 micrometers (μm) or less, thereby facilitating the following packaging processes. However, a lot of particles 18, such as silicon powder, are generated while the wafer backside grinding process is performed. The particles 18 are always attached on the wafer 16, and the upper surface 12a and the lower surface 12b of the suction pad 12, as shown in FIG. 1 and FIG. 2. Since the particles 18 are attached on the ground wafer 16 whose thickness is quite thin, and the suction pad 12 has a large and hard lower surface 12b, a cross-shaped flaw 20 is therefore formed in the ground wafer 16 when the ground wafer 16 is sucked by the suction pad 12 through vacuum suction. Unfortunately, once the cross-shaped flaw is formed in the wafer 16, the wafer 16 usually should be scrapped. Nevertheless, a lot of integrated circuits and metal interconnects have been manufactured in the wafer 16 before the wafer backside grinding process is performed, so that it not only reduces a production yield but also increases a production cost to scrap the wafer 16.